Family members of sailors wave as the U.S. Navy aircraft carrier USS Ronald Reagan arrives at a U.S. Navy base in Yokosuka, Japan south of Tokyo, Oct. 1, 2015. Photo: AP

The U.S. Pacific Fleet is shrinking even as the U.S. and its allies are facing challenges posed by China's growing military power.

U.S. Navy officials say the more advanced ships of today make up for the decline in numbers. But the Navy has also had to lengthen deployments and postpone maintenance to maintain its presence with fewer ships.

Peter Jennings, an expert at the Australian Strategic Policy Institute think tank, said the issue in peacetime is whether there are enough American vessels to reassure friends and allies.

"I think this is emerging as a serious long-term problem," he said.

The Pacific Fleet currently has 182 vessels, including combat ships like aircraft carriers as well as auxiliary and logistics vessels, said spokesman Cmdr. Clay Doss. That compares to 192 nearly two decades ago.

The Chinese People's Liberation Army Navy has more than 300 surface ships, submarines, amphibious ships and patrol craft, according to the Pentagon's Asia-Pacific Maritime Security Strategy report released in August.

This all comes as China has grown more aggressive in asserting claims to islands also claimed by U.S. allies, including the Philippines in the South China Sea and Japan in the East China Sea.

China sees the U.S. military presence in Asia as an attempt to contain it, said Denny Roy, a senior fellow at the East-West Center in Honolulu. Beijing sees itself as returning to its rightful and historical role as the pre-eminent cultural and political power in the region, he said.

Since December 2013, China has built what the U.S. estimates to be 3,000 acres of artificial islands in disputed areas of the South China Sea using sand dredged from the ocean floor.

China has said the islands are meant to help ships, fishermen and disaster relief.

Questions about whether the Pacific Fleet has enough resources are more of a reflection of regional anxieties than the Navy's actual capability, said its commander, Adm. Scott Swift.

"I'm very comfortable with the resources I have," Swift said.

He pointed to the USS Benfold, a guided missile destroyer upgraded with new ballistic missile defenses, as well as three new stealth destroyers, the DDG-1000, in the pipeline, as examples.

One consequence of a smaller fleet has been more time at sea. Retired Adm. Zap Zlatoper, who commanded the Pacific Fleet in the 1990s, said deployments longer than six months made it harder for the Navy to retain sailors. Ships now deploy for an average of seven to nine months, though the Navy plans to lower this to seven.

Ship conditions have also suffered. The USS Essex left an exercise with Australia early in 2011 and skipped another with Thailand the following year because it developed mechanical problems after delaying maintenance to stay at sea.

Bryan Clark, a senior fellow at the Center for Strategic and Budgetary Assessments, a Washington think tank, said these are signs the status quo is unsustainable.

In a November report, Clark outlined alternatives: build more ships, though this would require money Congress may not give the Navy, or deploy less, though the Pentagon has been reluctant to accept less of an overseas presence.

The other choices: keep more ships at overseas bases where they would be closer to where they operate or mix up how ships deploy. One example would be to send fewer escorts with an aircraft carrier.

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